Mechanized tree cutting may be accomplished with an articulated boom, or "knuckle boom" having a tree gripping and cutting head at its end, with the boom and head being driven by a hydraulic or other drive means. Tree cutting in restricted conditions requires the use of a device capable of reaching the head over or under obstacles such as utility lines or structures. Knuckle booms, grippers and fluid-driven saws are well known in the art, particularly for use in forestry operations. However, prior systems for gripping, handling and cutting trees suffer from not having a full range of control in all planes and are not generally suitable for removing trees or tree limbs in restricted conditions.
Typically, the cutting head in a boom-mounted device comprises a set of jaws adapted to grip a tree or log, and a saw or shears mounted to the head. The saw may comprise either a rotary or chain saw, and is pivotable or slidable relative to the jaws, in order to cut through the wood.
An example of a vehicle-mounted boom and cutting head is shown in Canadian Patent 1,224,704 (Gaitten), wherein an articulated boom mounted to a truck is provided with a cutting head at its free end. The cutting head includes a set of jaws for gripping a tree limb or trunk, and a longitudinally-slidable circular saw. However, the Gaitten device does not include a boom having a sufficient degree of articulation to reach around or behind obstructions.
Specific requirements apply to a tree cutting apparatus intended for use in restricted areas. The apparatus must be highly maneuverable, in order that the boom may reach over or under obstructions. The head should be capable of being oriented in any position, much like a human hand, in order to grip and cut a limb or tree in any position. In order to achieve these objects, the head may be mounted on an articulated boom, with a linkage that permits the head to both pivot and rotate in much the same manner as a human arm and wrist permit the hand to be positioned in any orientation. Preferably, the head should be continuously rotatable relative to the boom; this requires the use of a rotary drive coupling to permit the hydraulic lines or other drive and control means driving the head to be coupled with the boom. It is desirable as well for the saw or other cutting implement to pivot or be otherwise displaceable when not in use, in order to prevent damage thereto while the head is grappling the tree or limb. As well, it is desirable for the head to be adapted to gather brush and cut wood for disposal. Preferably, at least one of the segments of the boom should be extensible. As well, one of the joints may be provided with means to pivot by a full, or nearly full, 360 degrees in order to allow the operator to extend the head underneath obstructions, such as power lines, and bring the head upwardly and rearwardly around the obstruction.
It is desirable as well to provide means to prevent the saw blade from binding during and after the cutting process. Binding of the blade often results from uneven contact of the teeth of a gripping head with the wood during the cutting. Where the wood being gripped is uneven, one or more teeth may not touch the wood, allowing the section of wood to move as it is weakened by cutting. This problem may be addressed by providing a means whereby the teeth evenly grip the wood, regardless of its irregularities.
The saw in such a device may not be required if the device is to be used for purposes that do not require cutting, for example the emplacement of utility poles. For these applications, the head need not include a saw.
These and other objects are addressed by the present invention.